CVE-2024-11233: PHP Buffer Overflow Vulnerability

CVE-2024-11233 Overview

CVE-2024-11233 is a buffer overread vulnerability affecting PHP's convert.quoted-printable-decode stream filter. Due to an error in the filter's implementation, specially crafted data can trigger a one-byte buffer overread condition. This memory safety issue can result in application crashes (denial of service) or potentially disclose contents from adjacent memory areas, leading to information leakage.

Critical Impact

This vulnerability can be exploited remotely without authentication to cause denial of service conditions or leak sensitive memory contents from PHP applications processing untrusted input through the quoted-printable-decode filter.

Affected Products

• PHP 8.1.* before 8.1.31
• PHP 8.2.* before 8.2.26
• PHP 8.3.* before 8.3.14

Discovery Timeline

• 2024-11-24 - CVE CVE-2024-11233 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-11233

Vulnerability Analysis

The vulnerability resides in PHP's convert.quoted-printable-decode stream filter implementation. When processing certain malformed or specially crafted quoted-printable encoded data, the filter fails to properly validate buffer boundaries, resulting in a one-byte overread beyond the allocated buffer space.

This out-of-bounds read condition (CWE-122: Heap-based Buffer Overflow, CWE-787: Out-of-bounds Write) occurs during the decoding process where the filter interprets escape sequences in the quoted-printable format. The lack of proper bounds checking allows an attacker to read one byte past the intended buffer boundary.

The consequences of exploitation include application crashes when the overread accesses unmapped memory, or information disclosure when the adjacent memory contains sensitive data such as authentication tokens, session identifiers, or other application secrets.

Root Cause

The root cause stems from insufficient boundary validation in the quoted-printable decoding logic within PHP's stream filter implementation. The decoder fails to account for edge cases where the input data terminates in a manner that causes the parsing routine to read beyond the allocated input buffer by one byte.

Attack Vector

This vulnerability is exploitable over the network without requiring authentication or user interaction. An attacker can exploit this vulnerability by:

1. Sending specially crafted quoted-printable encoded data to a PHP application that uses the convert.quoted-printable-decode stream filter
2. The malformed data triggers the boundary validation error during decoding
3. The one-byte overread either causes a crash or returns adjacent memory contents
4. Information from the leaked memory may be extracted through response data or side-channel analysis

Applications that process user-supplied email content, file uploads, or any untrusted data through PHP's quoted-printable decoding functionality are potentially vulnerable.

Detection Methods for CVE-2024-11233

Indicators of Compromise

• Unexpected PHP application crashes or segmentation faults during content processing
• Abnormal memory access patterns in PHP processes handling quoted-printable encoded data
• Unusual error logs indicating buffer or memory access issues in stream filter operations
• Anomalous response data containing unexpected binary or garbled content

Detection Strategies

• Monitor PHP error logs for segmentation faults and memory-related crashes
• Implement application-level logging around stream filter operations to detect anomalous input patterns
• Deploy web application firewalls (WAF) with rules to detect malformed quoted-printable encoded payloads
• Use runtime application self-protection (RASP) solutions to detect out-of-bounds memory access attempts

Monitoring Recommendations

• Enable PHP error logging and monitor for repeated crashes in applications using stream filters
• Configure system-level crash monitoring to detect PHP process terminations
• Implement anomaly detection for unusual patterns in requests containing quoted-printable content
• Review application logs for evidence of information disclosure in response data

How to Mitigate CVE-2024-11233

Immediate Actions Required

• Upgrade PHP to version 8.1.31, 8.2.26, or 8.3.14 or later immediately
• Audit applications to identify usage of convert.quoted-printable-decode stream filter
• Consider temporarily disabling or replacing quoted-printable decoding functionality with alternative libraries until patching is complete
• Implement input validation and sanitization for any data processed through stream filters

Patch Information

PHP has released security patches addressing this vulnerability in versions 8.1.31, 8.2.26, and 8.3.14. Organizations should update to these patched versions immediately. Additional vendor-specific patches are available:

• PHP Security Advisory (GHSA-r977-prxv-hc43)
• Debian LTS Security Announcement
• NetApp Security Advisory

Workarounds

• Avoid using the convert.quoted-printable-decode stream filter on untrusted input until patches are applied
• Implement strict input length limits and validation before passing data to the vulnerable filter
• Consider using alternative quoted-printable decoding libraries that are not affected by this vulnerability
• Deploy network-level filtering to block potentially malicious quoted-printable encoded payloads

# Check current PHP version
php -v

# Update PHP on Debian/Ubuntu systems
sudo apt update && sudo apt upgrade php

# Update PHP on RHEL/CentOS systems
sudo yum update php

# Verify patched version is installed
php -v | grep -E "8\.(1\.3[1-9]|2\.2[6-9]|3\.1[4-9])"